Exercise Physiology: For Health, Fitness, and Performance_2 pdf

388 Cardiorespiratory Training Principles and Adaptations After studying the chapter, you should be able to: ■ Describe the exercise/physical activity recommendations of the American College of Sports Medi- cine, the Surgeon General’s Report, the ACSM/AHA Physical Activity and Public Health Guidelines, the National Association for Sport and Physical Education, and the CDC Expert Panel. Discuss why these reports contain different recommendations. ■ Discuss the application of each of the training principles in a cardiorespiratory training program. ■ Explain how the FIT principle is related to the overload principle. ■ Differentiate among the methods used to classify exercise intensity. ■ Calculate training intensity ranges by using different methods including the percentage of maxi- mal heart rate, the percentage of heart rate reserve, and the percentage of oxygen consumption reserve. ■ Discuss the merits of specifi city of modality and cross-training in bringing about cardiovascular adaptations. ■ Identify central and peripheral cardiovascular adaptations that occur at rest, during submaximal exercise, and at maximal exercise following an aerobic endurance or dynamic resistance training program. 13 Plowman_Chap13.indd 388Plowman_Chap13.indd 388 11/6/2009 9:04:10 PM11/6/2009 9:04:10 PM CHAPTER 13 • Cardiorespiratory Training Principles and Adaptations 389 INTRODUCTION In the last decade, physical fi tness–centered exercise pre- scriptions, which emphasize continuous bouts of rela- tively vigorous exercise, have evolved (for the nonathlete) into public health recommendations for daily moderate- intensity physical activity. Early scientifi c investigations that led to the development of training principles for the cardiovascular system almost always focused on the improvement of physical fi tness, operationally defi ned as an improvement of maximal oxygen consumption (V . O 2 max). Such studies formed the basis for the guide- lines developed by the American College of Sports Medi- cine (1978) as “the recommended quantity and quality of exercise for developing and maintaining fi tness in healthy adults.” These guidelines were revised in 1998 to “the recommended quantity and quality of exercise for devel- oping and maintaining cardiorespiratory and muscular fi tness, and fl exibility in healthy adults.” After 1978, these guidelines were increasingly applied not only to healthy adults intent on becoming more fi t but also to individuals seeking only health benefi ts from exercise training. Although evidence shows that health benefi ts accrue when fi tness is improved, health and fi tness are different goals, and exercise training and physical activity are differ- ent processes (Plowman, 2005). The quantity and quality of exercise required to develop or maintain cardiorespiratory fi tness may not be (and probably are not) the same as the amount of physical activity required to improve and main- tain cardiorespiratory health (American College of Sports Medicine, 1998; Haskell, 1994, 2005; Haskell et al., 2007; Nelson et al., 2007). Furthermore, most exercise science or physical education majors and competitive athletes who want or need high levels of fi tness can handle physically rigorous and time-consuming training programs. Such programs, however, carry a risk of injury and are often intimidating to those who are sedentary, elderly, or obese. Studies also suggest that different physical activity recommendations are warranted for children and adoles- cents. Thus, an optimal cardiovascular training program— maximizing the benefi t while minimizing the time, effort, and risk—varies with both the population and the goal. Table 13.1 summarizes recommendations for cardiorespi- ratory health and fi tness from leading authorities. APPLICATION OF THE TRAINING PRINCIPLES This chapter focuses on cardiovascular fi tness and car- diorespiratory function that can impact health. Thus, the exercise prescription recommendations of the ACSM, the physical activity guidelines from the Surgeon General’s Report (SGR, US DHS, 1996), and the Physical Activity and Public Health Guidelines sponsored jointly by the ACSM and the American Heart Association are discussed, along with the guidelines for children/adolescents. The emphasis will be on the changes that accompany a change in V . O 2 max. Additional information about physical fi tness and physical activity in relation to cardiovascular disease is presented in Chapter 15. Obviously, there are other goals for exercise pre- scription and physical activity guidelines in addition to cardiovascular ones. There is also some overlap in the cardiovascular benefi ts of physical activity/exercise with other health and fi tness areas, especially those pertain- ing to body weight/composition and metabolic function. Body weight aspects are discussed in the metabolic unit, and the recommendations for and benefi ts of resistance training and fl exibility are discussed in the neuromus- cular unit. The fi rst section of this chapter, focusing on how the training principles are applied for cardiorespiratory fi t- ness, relies heavily on the cardiorespiratory portion of the 1998 ACSM guidelines for healthy adults. Cardio- vascular fi tness is defi ned as the ability to deliver and use oxygen during intense and prolonged exercise or work. Cardiovascular fi tness is evaluated by measures of maximal oxygen consumption (V . O 2 max). Sustained exer- cise training programs using these principles to improve V . O 2 max are rarely included in the daily activities of chil- dren and adolescents. However, in the absence of more specifi c exercise prescription guidelines for younger individuals, these guidelines are often applied to adoles- cent athletes and youngsters in scientifi c training studies (Rowland, 2005). Specifi city Any activity that involves large muscle groups and is sus- tained for prolonged periods of time has the potential to increase cardiorespiratory fi tness. This includes such exercise modes as aerobics, bicycling, cross- country skiing, various forms of dancing, jogging, rollerblad- ing, rowing, speed skating, stair climbing or stepping, swimming, and walking. Sports involving high-energy, nonstop action, such as fi eld hockey, lacrosse, and soccer, can also positively benefi t the cardiovascular system (American College of Sports Medicine, 1998; Pollock, 1973). For fi tness participants, the choice of exercise modali- ties should be based on interest, availability, and risk of injury. An individual who enjoys the activity is more likely to adhere to the program. Although jogging or running may be the most time-effi cient way to achieve cardiorespi- ratory fi tness, these activities are not enjoyable for many individuals. They also have a relatively high incidence of overuse injuries. Therefore, other options should be available in fi tness programs. Cardiorespiratory Fitness The ability to deliver and use oxygen under the demands of intensive, pro- longed exercise or work. Plowman_Chap13.indd 389Plowman_Chap13.indd 389 11/6/2009 9:04:14 PM11/6/2009 9:04:14 PM 390 Cardiovascular-Respiratory System Unit TABLE 13.1 Physical Activity and Exercise Prescription for Health and Physical Fitness Modality Source Frequency Intensity Duration Cardiorespiratory Neuromuscular Surgeon General’s Report (1996) Most, if not all days of the week Moderate † Accumulate 30 min·d −1 Any physical activity burning ~150 kcal·d −1 or 2 kcal·kg·d −1 American College of Sports Medicine (1998) 3–5 d·wk −1 55*/65–90% HRmax 40*/50–85% HRR Continuous 20–60 min or intermittent (³10-min bouts) Rhythmical, aerobic, large muscles Dynamic resistance: 1 set of 8–12 (or 10–15*) reps; 8–10 lifts; 2–3 d·wk −1 40*/50–85% V . O 2 R Flexibility: Major muscle groups range of motion; 2–3 d·wk −1 ACSM/AHA (2007): Healthy adults 18–65 y 5 d·wk −1 3 d·wk −1 Moderate OR Vigorous 30 min 20 min 8–10 strength training exercises 12 repetitions, 2d·wk −1 ACSM/AHA (2007): Older adults As above 8–10 strength training exercises 10–15 repetitions, 2 d·wk −1 ; fl exibility exercises 2 d·wk −1 and balance exercises as needed NASPE (2004): Children 5–12 yr All, or most days Moderate to vigorous 60+ min·d −1 Intermittent, but several bouts >15 min Age-appropriate aerobic sports CDC Expert Panel: Children/ adolescents 6–18 yr Daily Moderate to vigorous 60+ min·d −1 Age appropriate (Strong et al., 2005), enjoyable, varied *Intended for least-fi t individuals. † Examples include touch football, gardening, wheeling oneself in wheelchair, walking at a pace of 20 min·mi −1 , shooting baskets, bicycling at 6 mi·hr −1 , social dancing, pushing a stroller 1.5 mi·30 min −1 , raking leaves, water aerobics, swimming laps. Sources: Haskell, W. L., I. Lee, R. R. Pate, et al.: Physical activity and public health: Updated recommendation for adults from the American College of Sports Medicine and the American Heart Association. Medicine and Science in Sports and Exercise. 39(8):1423–1434 (2007); Nelson, M. E., W. J. Rejeski, S. N. Blair, et al.: Physical activity and public health in older adults: Recommendation from the American College of Sports Medicine and the American Heart Association. Medicine and Science in Sports and Exercise. 39(8):1435–1445 (2007). Although many different modalities can improve cardiovascular function, the greatest improvements in performance occur in the modality used for training, that is, there is modality specifi city. For example, indi- viduals who train by swimming improve more in swim- ming than in running (Magel et al., 1975), and individuals who train by bicycling improve more in cycling than in running (Pechar et al., 1974; Roberts and Alspaugh, 1972). Modality specifi city has two important practical applications. First, to determine whether improvement is occurring, the individual should be tested in the modal- ity used for training. Second, the more the individual is Plowman_Chap13.indd 390Plowman_Chap13.indd 390 11/6/2009 9:04:14 PM11/6/2009 9:04:14 PM CHAPTER 13 • Cardiorespiratory Training Principles and Adaptations 391 muscles but not to habitually inactive ones. Other factors within exercising muscles such as mitochondrial density and enzyme activity also affect the body’s ability to reach a high V . O 2 max. Specifi city of modality operates because peripheral adaptations occur in the muscles that are used in the training. Thus, specifi c activities—or closely related activities that mimic the muscle action of the pri- mary sport—are needed to maximize peripheral adapta- tions. Examples of mimicking muscle action include side sliding or cycling for speed skating and water running in a fl otation vest for jogging or running. One study divided endurance-trained runners into three groups. One third continued to train by running, one third trained on a cycle ergometer, and one third trained by deep water running. The intensity, frequency, and duration of workouts in each modality were equal. After 6 weeks, performance in a 2-mi run had improved slightly (~1%) in all three groups (Eyestone et al., 1993). Thus, running performance was maintained by each of the modalities. On the other hand, arm ergometer training has not been shown to maintain training ben- efi ts derived from leg ergometer activity (Pate et al., 1978). Apparently, the closer the activities are in terms of muscle action, the greater the potential benefi t of cross-training. Table 13.2 lists several situations, in addition to the maintenance of fi tness when injured, in which cross- training may be benefi cial (Kibler and Chandler, 1994; O’Toole, 1992). Note that multisport athletes may or may not be limited to the sports in which they are com- peting. For example, although a duathlete needs to train for both running and cycling, this training will have the benefi ts of both specifi city and cross-training. In addi- tion, this athlete may also cross-train by doing other activities such as rollerblading or speed skating. Note also that cross-training can be recommended at any time for a fi tness participant to help avoid boredom. For a healthy competitive athlete, the value of cross- training is modest during the season. Cross-training is most valuable for single-sport competitive athletes during the transition (active rest) phase but may also be benefi cial during the general preparation phase of periodization. Overload Overload of the cardiovascular system is achieved by manipulating the intensity, duration, and frequency of the training bouts. These variables are easily remem- bered by the acronym FIT (F = frequency, I = inten- sity, and T = time or duration). Figure 13.1 presents the results of a study in which the components of overload were investigated relative to their effect on changes in V . O 2 max. As the most critical component, intensity will be discussed fi rst. concerned with sports competition rather than fi tness or rehabilitation, the more important the mode of exercise becomes. A competitive rower, for example, whether competing on open water or an indoor ergometer, should train mostly in that modality. Running, however, seems to be less specifi c than most other modalities; running forms the basis of many sports other than track or road races (Pechar et al., 1974; Roberts and Alspaugh, 1972; Wilmore et al., 1980). Although modality specifi city is important for com- petitive athletes, cross-training also has value. Originally, the term “cross-training” referred to the development or maintenance of muscle function in one limb by exercising the contralateral limb or upper limbs as opposed to lower limbs (Housh and Housh, 1993; Kilmer et al., 1994; Pate et al., 1978). Such training remains important, especially in situations where one limb has been injured or placed in a cast. As used here, however, the term “cross-training” refers to the development or maintenance of cardiovas- cular fi tness by training in two or more modalities either alternatively or concurrently. Two sets of athletes, in particular, are interested in cross-training. First, injured athletes, especially those with injuries associated with high-mileage running, who wish to prevent detraining. Second, an increasing number of athletes participate in multisport competitions such as biathlons and triathlons and need to be conditioned in each. Theoretically, both specifi city and cross-training have value for a training program. Any form of aerobic endur- ance exercise affects both central and peripheral cardiovas- cular functioning. Central cardiovascular adaptations occur in the heart and contribute to an increased ability to deliver oxygen. Central cardiovascular adaptations are the same in all modalities when the heart is stressed to the same extent. Thus, many modalities can have the same overall training benefi t by leading to central cardiovascu- lar adaptations. Peripheral cardiovascular adaptations occur in the vasculature or the muscles and contribute to an increased ability to extract oxygen. Peripheral cardiovascular adaptations are specifi c to the modality and the specifi c muscles used in that exercise. For example, additional capillaries will form to carry oxygen to habitually active Cross-training The development or maintenance of cardiovascular fi tness by alternating between or con- currently training in two or more modalities. Central Cardiovascular Adaptations Adaptations that occur in the heart that increase the ability to deliver oxygen. Peripheral Cardiovascular Adaptations Adaptations that occur in the vasculature or muscles that increase the ability to extract oxygen. Plowman_Chap13.indd 391Plowman_Chap13.indd 391 11/6/2009 9:04:15 PM11/6/2009 9:04:15 PM 392 Cardiovascular-Respiratory System Unit of 90–100% of V . O 2 max. In order to achieve such high intensity, training individuals may alternate work and rest intervals (interval training). At exercise levels greater than 100% (supramaximal exercise), in which the total amount of training that can be performed decreases, improvement in V . O 2 max is somewhat less than is seen at 90–100% V . O 2 max. Intensity Figure 13.1A shows the relationship between change in V . O 2 max and exercise intensity. In general, as exercise intensity increases, so do improvements in V . O 2 max. The greatest amount of improvement in V . O 2 max is seen fol- lowing training programs that utilize exercise intensities TABLE 13.2 Situations in Which Cross-Training Is Benefi cial Reason Fitness Participant Competitive Athlete Multisport participation General preparation phase, specifi c preparation phase, competitive phase Injury or rehabilitation; fi tness maintenance As needed As needed Inclement weather As needed As needed Baseline or general conditioning Always General preparation phase Recovery After intense workout After intense workout or competition Prevention of boredom and burnout Always Transition phase Source: Kibler, W. B., & T. J. Chandler: Sport-specifi c conditioning. American Journal of Sports Medicine. 22(3):424–432 (1994). 0 Frequency (sessions·wk –1 ) Duration (min·session –1 ) 35–45 15–25 23456 25–35 Initial fitness level VO 2 max (mL·kg –1 ·min –1 ) 50–60 30–40 40–50 Change in VO 2 max (mL·kg –1 ·min –1 ) 8 6 4 2 0 8 6 4 2 C B D Change in VO 2 max (mL·kg –1 ·min –1 ) 0 8 6 4 2 Change in VO 2 max (mL·kg –1 ·min –1 ) Intensity, % VO 2 max 50–70 90–100 8 6 4 2 0 A Change in VO 2 max (mL·kg –1 ·min –1 ) FIGURE 13.1. Changes in V . O 2 max Based on Frequency, Intensity, and Duration of Training and on Initial Fitness Level. Source: Wenger, H., A., & G. J. Bell. The interactions of intensity, frequency and duration of exercise training in altering cardiorespiratory fi tness. Sports Medicine. 3:346–356 (1986). Reprinted by permis- sion of Adis International, Inc. Plowman_Chap13.indd 392Plowman_Chap13.indd 392 11/6/2009 9:04:15 PM11/6/2009 9:04:15 PM CHAPTER 13 • Cardiorespiratory Training Principles and Adaptations 393 Example Calculate the predicted or estimated HRmax for a 28-year-old female with a normal body composition. HRmax = 220 − age = 220 − (28 yr) = 192 b·min −1 If the female is obese, her estimated HRmax is HRmax = 200 − (0.5 × age) = 200 − (0.5 × 28 yr) = 186 b·min −1 Once the HRmax is known or estimated, the %HRmax is calculated as follows: Target exercise heart rate (TExHR) = maximal heart rate (b·min −1 ) × percentage of maximal heart rate (expressed as a decimal) or TExHR = HRmax × %HRmax 13.2 1. Determine the desired intensity of the workout. 2. Use Table 13.3 to fi nd the %HRmax associated with the desired exercise intensity. 3. Multiply the percentages (as decimals) times the HRmax. Example Determine the appropriate HR training range for a moderate workout for a nonobese 28-year-old individual using the HRmax. 1. Determine the HRmax: 220 − 28 = 192 b·min −1 2. Determine the desired intensity of the workout. Table 13.3 shows 55–69% of HRmax corresponds to a moderate workout. 3. Multiply the percentages (as decimals) times the HRmax for the upper and lower exercise limits. Thus HRmax 192 192 desired intensity (decimal) × 0.55 × 0.69 Target HR Range (rounded) 106 133 Thus, an HR of 106 b·min −1 represents 55% of HRmax and an HR of 133 b·min −1 represents 69% of HRmax. To exercise between 55% and 69% of HRmax, a moder- ate workload, this individual should keep her heart rate between 106 and 133 b·min −1 . It is always best to provide the potential exerciser with a target heart rate range rather than a threshold heart rate. In fact, the term “threshold” may be a mis- nomer since no particular percentage has been shown Intensity, both alone and in conjunction with duration, is very important for improving V . O 2 max. Intensity may be described in relation to heart rate, oxygen consump- tion, or rating of perceived exertion (RPE). Laboratory studies typically use V . O 2 for determining intensity, but heart rate and RPE are more practical for individuals out- side the laboratory. Table 13.3 includes techniques used to classify intensity and suggests percentages for very light to very heavy activity (American College of Sports Medicine, 1998). Note that these percentages and classi- fi cations are intended to be used when the exercise dura- tion is 20–60 minutes and the frequency is 3–5 d·wk −1 . Heart Rate Methods Exercise intensity can be expressed as a percentage of either maximal heart rate (%HRmax) or heart rate reserve (%HRR). Both techniques, explained below, require HRmax to be known or estimated. The methods are most accurate if the HRmax is actually measured during an incremental exercise test to maximum. If such a test cannot be performed, HRmax can be esti- mated. ACSM recommends the following traditional, empirically based, easy formula using age despite the equation’s large (±12–15 b·min −1 ) standard deviation (Wallace, 2006). This large standard deviation, based on population averages, means that the calculated value may either overestimate or underestimate the true HRmax by as much as 12–15 b·min −1 (Miller et al., 1993; Wallace, 2006). maximal heart rate (b·min -1 ) = 220 − age (yr) 13.1a For obese individuals, the following equation is more accurate (Miller et al., 1993): maximal heart rate (b·min -1 ) = 200 − [0.5 × age (yr)] 13.1b For older adults, the following equation is more accurate (Tanaka et al., 2001): maximal heart rate (b·min -1 ) = 208 − [0.7 × age (yr)] 13.1c As indicated in Chapter 12, HRmax is independent of age between the growing years of 6 and 16. This means that the “220 − age (yr)” equation cannot be used for youngsters at this age (Rowland, 2005). During this age span for both boys and girls, the average HRmax resulting from treadmill running is 200–205 b·min −1 . Values obtained during walking and cycling are typi- cally 5–10 b·min −1 lower at maximum. As with adults, measured values are always preferable but may not be practical. Therefore, the value estimated for HRmax for children and young adolescents should depend on modality rather than age. Plowman_Chap13.indd 393Plowman_Chap13.indd 393 11/6/2009 9:04:15 PM11/6/2009 9:04:15 PM 394 Cardiovascular-Respiratory System Unit Target exercise heart rate (b·min −1 ) = [heart rate reserve (b·min −1 ) × percentage of heart rate re- serve (expressed as a decimal)] + resting heart rate (b·min −1 ) or TExHR = (HRR × %HRR) + RHR 13.4 Determine the appropriate HR range for a moderate workout for a normal-weight, 28-year-old individual using the HRR method, assuming a RHR of 80 b·min −1 . 1. Determine the HRR: 192 b·min −1 − 80 b·min −1 = 112 b·min −1 2. Determine the desired intensity of the workout. Again, using Table 13.3, 40–59% of HRR corre- sponds to a moderate workout. This reinforces the point that the %HRmax does not equal %HRR. 3. Multiply the percentages (as decimals) for the upper and lower exercise limits by the HRR. Thus HRR 112 112 desired intensity (decimal) × 0.4 × 0.59 45 66 4. Add RHR as follows: 45 66 resting HR ±80 ±80 target HR training range (b·min −1 ) 125 146 continued Example to be a minimally necessary threshold for all individuals in all situations (Haskell, 1994). Additionally, a range allows for the heart rate drift that occurs in moderate to heavy exercise after about 30 minutes and for varia- tions in weather, terrain, fl uid replacement, and other infl uences. The upper limit serves as a boundary against overexertion. Alternatively, a target heart rate range can be calcu- lated as a %HRR, a technique also called the Karvonen method. It involves additional information and calcula- tions but has the advantage of considering resting heart rate. The steps are as follows: 1. Determine the HRR by subtracting the resting heart rate from the HRmax: Heart rate reserve (b·min −1 ) = maximal heart rate (b·min −1 ) − resting heart rate (b·min −1 ) or HRR = HRmax − RHR 13.3 The resting heart rate is best determined when the individual is truly resting, such as immediately on awakening in the morning. However, for purposes of exercise prescription, this can be a seated or standing resting heart rate, depending on the exercise posture. Heart rates taken before an exercise test are anticipa- tory, not resting, and are higher than actual resting heart rate. 2. Choose the desired intensity of the workout. 3. Use Table 13.3 to fi nd the %HRR associated with the desired exercise intensity. 4. Multiply the percentages (as decimals) for the upper and lower exercise limits by the HRR and add RHR using Equation 13.4. TABLE 13.3 Classifi cation of Intensity of Exercise Based on 20–60 minutes of Endurance Training Relative Intensity Classifi cation of intensity %HRmax %HRR/%V . O 2 R Borg RPE Very light <35 <20 <10 Light 35–54 20–39 10–11 Moderate 55–69 40–59 12–13 Hard 70–89 60–84 14–16 Very hard ³90 ³85 17–19 Maximal 100 100 20 Source: American College of Sports Medicine: Position stand on the recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fi tness and fl exibility in healthy adults. Medicine and Science in Sports and Exercise. 30(6):975–985 (1998). Plowman_Chap13.indd 394Plowman_Chap13.indd 394 11/6/2009 9:04:17 PM11/6/2009 9:04:17 PM CHAPTER 13 • Cardiorespiratory Training Principles and Adaptations 395 Target exercise oxygen consumption (mL·kg −1 ·min −1 ) = [oxygen consumption reserve (mL·kg −1 ·min −1 ) × percentage of oxygen consumption reserve (ex- pressed as a decimal)] + resting oxygen consump- tion (mL·kg −1 ·min −1 ) or TExV . O 2 = (V . O 2 R × %V . O 2 R) + V . O 2 rest 13.6 Use these steps to calculate training intensity with this method: 1. Choose the desired intensity of the workout. 2. Use Table 13.3 to fi nd the %V . O 2 R for the desired exercise intensity. 3. Multiply the percentage (as a decimal) of the desired intensity times the V . O 2 max. 4. Add the resting oxygen consumption to the obtained values. Note that this may be an individually measured value or the estimated 3.5 mL·kg −1 ·min −1 that repre- sents 1 metabolic equivalent (MET). 5. Because oxygen drifts, as does heart rate, it is best to use a target range. Thus, a HR of 125 b·min −1 represents 40% of HRR and an HR of 146 b·min −1 represents 59% of HRR. So, in order to be exercising between 40% and 59% of HRR, a moderate workload, this individual should keep her heart rate between 125 and 146 b·min −1 . Example (continued) This heart rate range (125−146 b·min −1 ), although still moderate, is different from the one calculated by using %HRmax (106−133 b·min −1 ) because the resting heart rate is considered in the HRR method. Work through the problem presented in the Check Your Comprehension 1 box, paying careful attention to the infl uence of resting heart rate when determining the train- ing heart rate range using the HRR (Karvonen) method. CHECK YOUR COMPREHENSION 1 Calculate the target HR range for a light workout for two normal-weight individuals, using the %HRmax and %HRR methods and the following information. Age RHR Lisa 50 62 Susie 50 82 Check your answer in Appendix C. HRmax declines in a rectilinear fashion with advancing age in adults. Thus, the heart rate needed to achieve a given intensity level, calculated by either the HRmax or the HRR method, decreases with age. Figure 13.2 exem- plifi es these decreases for light, moderate, and heavy exer- cise using the %HRR method and the expected benefi ts within each range from age 20 to 70 years. Oxygen Consumption/%V . O 2 R Methods In a laboratory setting where an individual has been tested for and equipment is available for monitoring V . O 2 dur- ing training, %V . O 2 R may be used to prescribe exercise intensity. Oxygen reserve is parallel to HRR in that it is the difference between a resting and a maximal value. It is calculated according to the formula: 13.5 Oxygen consumption reserve (mL·kg −1 ·min −1 ) = maximal oxygen consumption (mL·kg −1 ·min −1 ) – resting oxygen consumption (mL·kg −1 ·min −1 ) or V . O 2 R = V . O 2 max - V . O 2 rest Target exercise oxygen consumption is then deter- mined by the equation: Age (yr) Health benefits Light Moderate Hard 20% HRR 40% HRR 60% HRR 20 30 40 50 60 70 HR (b·min –1 ) 180 170 160 150 140 130 120 110 100 90 85% HRR Very light Health benefits Health & fitness benefits Health & fitness benefits Health & fitness benefits Very hard FIGURE 13.2. Age-Related Changes in Training Heart Rate Ranges Based on HRR (Karvonen) Method. Note: Calculations are based on RHR = 80 b·min −1 , HRmax = 220 − age. Plowman_Chap13.indd 395Plowman_Chap13.indd 395 11/6/2009 9:04:18 PM11/6/2009 9:04:18 PM 396 Cardiovascular-Respiratory System Unit either %HRmax or %HRR when prescribing exercise intensity for children and adolescents, and not make any equivalency assumption with %V . O 2 . Table 13.4 shows how long one can run at a specifi c percentage of maximal oxygen consumption. The Check Your Comprehension 2 box provides an example of how this information can be used in training and competi- tion. Take the time now to work through the situation described in the box. CHECK YOUR COMPREHENSION 2 Four friends meet at the track for a noontime workout. Their physiological characteristics are as follows. (The estimated V . O 2 max values have been calculated from a 1-mi running test.) Individual Age (yr) Estimated V . O 2 max (mL·kg −1 ·min −1 ) Resting HR (b·min −1 ) Janet 23 52 60 Juan 35 64 48 Mark 22 49 64 Gail 28 56 58 The following oxygen requirements have been calcu- lated for a given speed based on the equations that are presented in Appendix B. Speed (mph) Oxygen Requirement (mL·kg −1 ·min −1 ) 4 27.6 5 30.3 6 35.7 7 41.0 8 46.4 9 51.7 The friends wish to run together in a moderate workout. Assume temperate weather conditions. 1. At what speed should they be running? 2. What heart rate should be achieved by each runner at that pace? Check your answers with the ones provided in Appendix C. Rating of Perceived Exertion Methods The third way exercise intensity can be prescribed is by a subjective impression of overall effort, strain, and fatigue during the activity. This impression is known as a rating of perceived exertion. Perceived exertion is typically measured using either Borg 6–20 RPE scale or the revised 0−10+ Category Ratio Scale (Borg, 1998). Basing the intensity of a workout on %V . O 2 R is not very practical because most people do not have access to the needed equipment. However, the technique can be modifi ed for individuals who wish to use it. First, one can use the formula in Appendix B (The Calculation of Oxygen Consumed Using Mechanical Work or Speed of Movement) to solve for the workload (velocity of level or inclined walking or running; resistance for arm or leg cycling; height or cadence for bench stepping). Then, the prescription can be based on minutes per mile, cadence of stepping at a particular height, or load setting at a specifi c revolutions-per-minute pace. Because the oxygen cost of submaximal exercise is higher for children and changes as they age and grow, this technique is rarely used for chil- dren (Strong et al., 2005). A second practical use of the V . O 2 R approach is based on the direct relationship between heart rate and oxygen consumption. Look closely again at Table 13.3. Note that the column for %V . O 2 R is also the column for %HRR; that is, any given %HRR has an equivalent %V . O 2 R in adults. For example, an adult who is working at 50% HRR is also working at 50% V . O 2 R. Therefore, heart rate can be used to estimate oxygen consumption when an individual is training or competing. The equivalency between %V . O 2 R and %HRR has been demonstrated experimentally in both young and older adult males and females, and for the modalities of cycle ergometry and treadmill walking and running (Swain, 2000). Although there is also a rectilinear relationship between %HRR and %V . O 2 R in children and adolescents, this relationship is not the same as for adults. In children and adolescents, the two percentages are not equal. In a recent study, 50–85%V . O 2 R was found to equate with 60–89% HRR in boys and girls 10–17 years of age (Hui and Chan, 2006). Therefore, it is probably best to simply use TABLE 13.4 Time a Selected %V . O 2 max Can Be Sustained During Running %V . O 2 max Time (min) 100.00 8–10 97.5 15 90 30 87.5 45 85 60 82.5 90 80 120–210 Source: Daniels, J., & J. Gilbert: Oxygen Power: Performance Tables for Distance Runners. Tempe, AZ: Author (1979). Plowman_Chap13.indd 396Plowman_Chap13.indd 396 11/6/2009 9:04:19 PM11/6/2009 9:04:19 PM CHAPTER 13 • Cardiorespiratory Training Principles and Adaptations 397 if an individual normally works out at 75% HRmax on land, the prescription for an equivalent workout in the water should be 65% HRmax. Another way to achieve the adjustment, if an estimated HRmax is used, is to start with 205 b·min −1 minus age rather than 220 b·min −1 minus age. Either of these changes should effectively reduce the RPE as well. Regardless of the method chosen to prescribe exercise intensity, always consider three factors: 1. Exercise intensity should generally be prescribed within a range. Many activities require different lev- els of exertion throughout the activity. This is par- ticularly true of games and athletic activities, but it also applies to activities like jogging and bicycling, in which changes in terrain can greatly affect exertion. In addition, a range allows for cardiovascular and oxygen consumption drifts during prolonged exercise. 2. Exercise intensity must be considered in conjunction with duration and frequency. a. Intensity cannot be prescribed without regard to duration. These two variables are inversely related: In general, the more intense an activity is, the shorter it should be. b. The appropriate intensity of exercise also depends on the individual’s fi tness level and, to some extent, the point within his or her fi tness program. Table 13.5 presents and compares both scales. The RPE scale is designed so that these perceptual ratings rise in a rectilinear fashion with heart rate, oxygen consump- tion, and mechanical workload during incremental exercise; thus, it is the primary scale used for cardio- vascular exercise prescription (Table 13.3). The CR-10 scale increases in a positively accelerating curvilinear fashion and closely parallels the physiological responses of pulmonary ventilation and blood lactate. Chapter 5 describes the use of these scales for metabolic exercise prescription. Both the Borg RPE and the CR-10 scales are intended for use with postpubertal adolescents and adults. Because children (~6–12 yr) have diffi culty consistently assigning numbers to words or phrases to describe their exercise-related feelings, Robertson et al. (2002) devel- oped the Children’s OMNI Scale of Perceived Exertion. The OMNI Scale uses numerical, pictorial, and verbal descriptors. The original scale, depicted in Figure 13.3, was validated for cycling activity. Since then, variations have been developed for walking/running (Utter et al., 2002) and stepping (Robertson et al., 2005). Children have been shown to be able to self-regulate their cycling exercise intensity using the OMNI Scale (Robertson et al., 2002). In addition, observers can determine children’s exercise intensity using the OMNI Scale ( Robertson et al., 2006). This could be very helpful for teachers. The classifi cation of exercise intensity and the cor- responding relationships among %HRmax, %V . O 2 R, %HRR, and RPE presented in Table 13.3 have been derived from and are intended for use with land-based activities in moderate environments. Whether a water activity is performed horizontally, as in swimming, or vertically, as in running or water aerobics, postural and pressure changes shift the blood volume centrally and cause changes in blood pressure, cardiac output, resistance, and respiration. Although the magnitude of changes in the cardiovascular system var- ies considerably among individuals, the most consistent changes are lower submaximal HR (8–12 b·min −1 ) at any given V . O 2 , a lower HRmax (~15 b·min −1 ), and a lower V . O 2 max when exercise is performed in the water. A greater reliance on anaerobic metabolism is evident, and the RPE is higher in water than at the same workload on land (Svedenhag and Seger, 1992). The lower HR is probably a compensation for the increased stroke vol- ume (SV) when blood is shifted centrally. As a result, the HR prescription should be about 10% lower for water workouts than for land-based workouts. For example, TABLE 13.5 Scales for Ratings of Perceived Exertion RPE Scale CR-10 Scale 6 0.0 7 Very, very light 0.0 8 0.5 Just noticeable 9 Very light 1.0 Very weak 10 1.5 11 Fairly light 2.0 Light/weak 12 3.0 Moderate 13 Somewhat hard 3.5 4.0 Somewhat strong 14 4.5 5.0 15 Hard 5.5 6.0 16 6.5 Very strong 7.0 17 Very hard 7.5 8.0 18 9.0 19 Very, very hard 10.0 Extremely strong 20 10 + (~r12) Highest possible Rating of Perceived Exertion A subjective impres- sion of overall physical effort, strain, and fatigue during acute exercise. 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